The topical application of benzoyl peroxide has been found to be effective in the treatment of acne vulgaris, as disclosed for example in U.S. Pat. No. 3,535,422, issued Oct. 20, 1970 to Richard M. Cox and Leonard R. Ciafo and assigned to Steifel Laboratories, Inc. Benzoyl peroxide compositions have become the leading anti-acne compositions due to the antimicrobial effect of benzoyl peroxide on Propionobacterium Acne, the main anaerobic acne causing bacteria. Generally the benzoyl peroxide is topically applied as a suspension containing from about 2.5 to about 10% w/w benzoyl peroxide.
However, the effectiveness of the benzoyl peroxide in the treatment of acne has proven to be a function of the stability of the benzoyl peroxide and the benzoyl peroxide composition applied to the affected region. Benzoyl peroxide is, however, very unstable in solution and degrades rapidly to inactive benzoic acid. Prior benzoyl peroxide compositions have decomposed rapidly during storage and therefore do not have a reasonable shelf life. Yet, decomposition of benzoyl peroxide when in contact with skin is highly desirable since it is the oxidizing effect of the free radicals produced on decomposition that provides the desired anti-acne effect.
It is therefore highly desirable to obtain a benzoyl peroxide composition which is stable during storage and yet decomposes readily on contact with skin. Moreover, it would be even more desirable that such a benzoyl peroxide composition be clear since benzoyl peroxide itself is a colorless, odorless crystalline solid.